Medical devices

ABSTRACT

An embryo transfer catheter or other medical device has a shaft extruded with two layers. The outer layer is relatively thick and contains gas bubbles sufficient to increase the visibility of the catheter under ultrasound observation but with a density that allows material within the catheter to be viewed by the eye. The inner layer is relatively thin and is free of bubbles so that it provides a smooth bore to the catheter.

BACKGROUND OF THE INVENTION

This invention relates to medical devices.

The invention is more particularly concerned with catheters or the like, that are visible under ultrasound observation.

Ultrasound imaging equipment is increasingly being used during surgical procedures to monitor the location of a device within the body. The visibility of a device under ultrasound depends on various factors including the difference between the acoustic impedance of the material of the device and that of the surrounding medium, such as the patient tissue or body fluid w thin which the device is located. This difference is relatively low with plastic devices such as catheters and may make conventional catheters difficult to locate. Even devices of metal, such as needles, present problems of visibility under ultrasound observation because of the directional nature of the reflections. In some orientations a metal needle may be clearly visible but in other orientations it may be considerably less visible.

Attempts have been made to increase the visibility of medico-surgical devices under ultrasound observation in various ways. The surface of the device may be modified, such as by forming grooves or indentations in its surface. A reflective coating may be applied to the device, such as incorporating bubbles, as described in WO98/19713 and EP0624342. Alternatively, a metal marker may be secured to a plastics catheter. GB2379610 describes a catheter where the wall is made entirely of a plastics including gas bubbles or where bubble-containing material is in a stripe occupying only a part of the circumference. Although this latter form of catheter has various advantages, it has been found that there is a tendency for the surface of the bore through the catheter to be interrupted by small protrusions where the bubbles break the surface. In some applications, such as for embryo transfer, It is important that the bore of the catheter is as smooth as possible so any interruption of this is a disadvantage. In other applications it may be important instead for the outer surface to be as smooth as possible, or for both the outer and inner surface to be smooth.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative medical device.

According the present invention there is provided a medical device having an elongate portion of plastics material, the portion being extruded with at least a first, inner layer and a second layer on the outside of the inner layer one of the layers being substantially free of gas bubbles and the other of the layers including gas bubbles dispersed within it to increase the visibility of the device under ultrasound imaging.

The layer substantially free of gas bubbles may be thinner than the other layer. The layer substantially free of gas bubbles may be the inner layer. The second layer may provide an outer surface of the catheter. The device may include a third layer on the outside of the second layer. The second layer may contain gas bubbles and the first and third layers may be substantially free of gas bubbles. The bubbles may be in a region extending around the entire circumference of the device. The bubbles preferably extend in a continuous region along the length of the device. The gas bubbles may have a size in the range 0.1 μ to 300 μ, preferably having a size in the range 1 μ to 50 μ and roost preferably having a size in the range 5 μ to 10 μ. The gas bubbles may be provided by gas-filled polymer microspheres. The device may be a catheter having a bore extending along its length. The inner layer may have an inner surface providing the bore of the catheter. The plastics material is preferably transparent to the eye, the density of bubbles being such as to permit material within the catheter to be viewed by the eye.

An embryo-transfer catheter and its method of manufacture, according to the present invention, will now be described, by way of example, with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevation view of the catheter;

FIG. 2 is a sectional side elevation view of the catheter of FIG. 1 to a larger scale;

FIG. 3 is a cross-section view of the catheter along the line III-III of FIG. 2;

FIG. 4 illustrates schematically manufacture of the catheter;

FIG. 5 is a sectional side elevation view of a part of an alternative catheter; and

FIG. 6 is a cross-section view of the catheter of FIG. 5 along the line VI-VI.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first to FIGS. 1 to 3, the catheter comprises art elongate portion in the form of a flexible shaft 1 and a hub 2 joined at the rear end of the shaft. The shaft 1 has a circular section and a bore 10 extending along its length. The shaft 1 opens at its forward, right-hand, patient end 11, which is atraumatically rounded.

The shaft 1 is extruded in two layers 12 and 13. The first, inner layer 12 is of a clear, transparent polyurethane material and is free of gas bubbles so that its inner surface 14, providing the surface of the bore 10, is completely smooth. The second layer 13 is formed around the entire circumference of the first layer 12 and its outer surface 15 provides the outer surface of the catheter. The second layer 13 incorporates small, gas-filled bubbles 22 the size and distribution of which are selected to increase the visibility of the catheter under ultrasound observation. Typically, the gas bubbles have a diameter in the range of about 0.1 μ to 300 μ, preferably being between 1 μ and 50 μ with the most preferred range being about 5 μ to 10 μ. The bubbles 22 extend uniformly through the thickness and around the circumference of the second layer 13 and may be spherical or of any other regular or irregular shape. The second layer 13 is preferably made from the same plastics material as the first layer and the gas bubbles are preferably provided by incorporating gas-filled polymer microspheres such as of the kind sold under the trade mark Expancel (“Expancel” is a registered trade mark of Akzo Nobel). The bubble-filled layer 13 is preferably as thick as possible so as to increase the visibility of the catheter under ultrasound observation. The inner layer 12 may he relatively in since its purpose is solely to provide a smooth inner surface for the catheter.

The hub 2 serves to make connection with the shaft 1 and is moulded from a rigid, transparent plastics material, being subsequently bonded with the rear end of the shaft.

The shaft 1 is extruded in the manner shown in FIG. 4 using an extrusion machine 20. The machine 20 has two extrusion heads 21 and 22, winch are supplied respectively with a polyurethane material 23 and with a polyurethane material 24 containing hollow microspheres. The two materials 23 and 24 are heated and supplied to the respective extrusion heads 21 and 22 so that tubing is formed with the bubble-filled material 24 coextruded as the outer layer 13 about the outside of the inner layer 12, which is of the bubble-free material 23. The shaft 1 can he extruded continuously at low cost, without the need for any subsequent operations apart from attaching the hub 2 and end forming the patient end tip 11.

The bubbles could be formed in various other ways, such as by injecting gas into the melt. Alternatively, chemical foaming agents could be added to the plastics material, such as: azocarbonomides, dinitrosopentmethelyene-tetramine, benzenephonohydrazine, 4,4 oxybis(benzenephonohydrazine), NN¹dimethyl-NN¹ dinitrosoterephthalamide, azoisobutyronitrile, sodium bicarbonate, terephthalazide or trihydrazinatrazine. Another way of forming the gas bubbles would be by incorporating a liquid into the plastics melt which volatises during the melt process. Alternatively, solid powdered dry ice (carbon dioxide) could be incorporated into the melt so that the particles of dry ice become gas bubbles during the forming process. It might be possible to use other solids which undergo sublimation in this way. The bubbles could be formed directly as a result of chemical reaction during polymerisation and or alternatively during cross-linking. The bubbles could be formed mechanically by whipping the plastics in a liquid form, such as in the manner used to form latex foam. Alternatively, small particles of a soluble material could be added to the plastics melt and subsequently dissolved away.

The babble-filled layer need not provide the outer surface of the catheter, especially where the outer surface of the catheter needs to be smoother than can be provided by a bubble layer. Instead, as shown in FIGS. 5 and 6, the bubble-filled layer 113 could be sandwiched between an inner layer 112 and a third, outer layer 116, the inner and outer layers being of the same material and being free of bubbles. Preferably, the inner layer 112 and the outer layer 116 are relatively thin and the middle, bubble-filled layer 113 is relatively thick, to maximise the ultrasound reflecting properties of the catheter. This three-layer tube is also made by co-extruding the three layers with one another. Alternatively, where it was necessary for the outer surface of the catheter to be smooth and there was no need for the bore to be smooth, the catheter could just have two layers where the outer layer was thin and bubble-free and the inner layer was thicker and contained bubbles.

The catheter could have any number of additional layers with one or more layers containing bubbles.

Catheters according to the present invention can be made having good visibility under ultrasound imaging without producing multiple echoes. They can produce a good image regardless of the orientation of the catheter shaft. The shaft can be made sufficiently transparent to ultrasound energy to enable material flowing along the bore of the catheter to be observed on the ultrasound image.

Because the catheter does not require any coating or separate marker there is no need for subsequent assembly operations and there is no risk of detachment. The catheter can be made of conventional, medically-approved materials so does riot present any new risk to the patient. The outer surface of the three-layer catheter can be smooth so the catheter can be inserted or slid through an outer tube with low friction. A smooth bore can be provided to a catheter to ensure free flow along the bore, which can be important where the catheter is used to transfer embryos. In other applications, a smooth inner surface may reduce the accumulation of biofilm in the catheter. The catheter can be made without the need for metal components, which can be an advantage where the catheter is used while the patient is being viewed by magnetic imaging techniques. The catheter can be completely transparent to x-rays or the plastics from which it is formed could incorporate an x-ray opaque filler, such as barium sulphate.

The bubble size and density can be selected so that the optical transparency of the plastics forming the shaft remains sufficient to enable material flowing along the shaft to be viewed by the eye.

It is not essential for the bubbles to be provided around the entire circumference of the bubble-containing layer, instead, the bubbles could just be provided along a longitudinal stripe in the layer. This arrangement can be used where the shaft needs to have increased clarity so that material within the catheter can be seen by the eye. Alternatively, the bubbles could be contained around the entire circumference of the layer apart from a bubble-free longitudinal strip. The bubble region need not be continuous along the length of the catheter. Instead, discrete separate regions with bubbles could be separated from one another along the length of the catheter by regions without bubbles. A shaft for such a catheter could be made by blowing gas into the plastics forming the bubble layer and by interrupting the gas flow. Where the bubbles are contained within a stripe, this could be interrupted to make it discontinuous by extruding the stripe using two auxiliary extruders, one having material with hollow microspheres and the other having material without the microspheres. Alternate extruders would be switched on and off so that the stripe could have sections containing bubbles separated from one another by sections without bubbles. A catheter having a layer with an interrupted bubble region may give a clearer ultrasound indication of movement of the catheter along its length and may also enable clearer observation of material flowing along the catheter both by ultrasound and by the eye.

The invention is not confined to catheters but could be used in other medical devices such as cables and medical devices without a bore, or with more than one bore. 

1-18. (canceled)
 19. A medical device usable in ultrasound imaging having an extruded elongate portion of plastics material consisting of a first inner layer of a plastics material with a second layer of a plastics material formed around the inner layer, wherein one of said layers is extruded substantially free of gas bubbles and the other of said layers is extruded to include gas bubbles dispersed within the plastics material to increase the visibility of the medical device under ultrasound imaging.
 20. The medical device of claim 19, wherein said elongate portion is a catheter having a bore defined by the inner wall of said inner layer; and wherein said inner layer is the one layer of plastics material substantially free of gas bubbles.
 21. The medical device of claim 20, wherein the elongate portion is sufficiently transparent to ultrasound energy to enable material flowing along the bore to be observed on the ultrasound image.
 22. The medical device of claim 19, wherein the gas bubbles in said other layer are in discrete separate regions along the length of said elongate portion.
 23. The medical device of claim 19, wherein said elongate portion is a catheter having one and other ends, said elongate portion having a hub joined to one of said one and other ends.
 24. The medical device of claim 19, wherein the gas bubbles have a size in the range 0.1 μ to 300 μ.
 25. The medical device of claim 19, wherein the gas bubbles are provided by gas-filled polymer microspheres.
 26. A medical device usable in ultrasound imaging having an elongate portion of plastics material consisting of a first inner layer of a plastics material and a second layer of a plastics material coextruded with one another with said second layer formed around said first inner layer, wherein one of said layers is extruded substantially free of gas bubbles and the other of said layers is extruded to include gas bubbles dispersed within the plastics material to increase the visibility of the medical device under ultrasound imaging.
 27. The medical device of claim 26, wherein the other of said layers provides a main substrate of the device, and wherein said layer substantially free of gas bubbles is thinner than said other layer such that the layer containing gas bubbles is covered at a surface by the thinner of the layers.
 28. The medical device of claim 26, wherein said elongate portion is a catheter having one and other ends with a bore defined by the inner wall of said inner layer, the catheter having a hub joined to one of said one and other ends.
 29. In a surgical procedure wherein an ultrasound imaging equipment is used to monitor the location of a medical device within a patient, the equipment able to monitor said medical device due to said medical device having an elongate portion of a first inner layer of plastics material and a second layer of plastics material formed around the inner layer, wherein said first and second layers of plastics material are coextruded from respective plastics materials with one of said layers being extruded to be substantially free of gas bubbles and the other of said layers being extruded to include gas bubbles dispersed in said other layer, wherein as said medical device is placed into and within the patient, the location of said medical device is monitored by said ultrasound imaging equipment, the location of said medical device within the patient being more readily observable due to the other layer of said medical device providing an increase in the visibility of said medical device under ultrasound imaging.
 30. The procedure of claim 29, wherein said medical device is a catheter and wherein the elongate portion of the catheter has a third layer coextruded with said one and other layers so that said other layer with the gas bubbles is formed about said first inner layer and said third layer is formed about said other layer to provide the catheter with a smooth inner wall and a smooth outer wall.
 31. The procedure of claim 29, wherein said elongate portion is a catheter having a bore defined by the inner wall of said inner layer, and wherein said inner layer is the one layer of plastics material substantially free of gas bubbles.
 32. The procedure of claim 31, wherein said elongate portion is an embryo transfer catheter, and wherein the plastics materials are sufficiently transparent to ultrasound energy to enable an embryo moving along the catheter to be monitored by said ultrasound imaging equipment.
 33. A method of manufacturing a medical device usable for ultrasound imaging, comprising the steps of: supplying a first plastics material to an extrusion machine; supplying a second plastics material to the extrusion machine; coextruding the first and second plastics materials with one another to form an elongate tubing with a first inner layer of a plastics material forming the inner wall of the tubing to define a bore of the tubing and a second layer of a plastics material formed around the inner layer; wherein one of the coextruded first and second plastics materials is substantially free of gas bubbles and the other of the coextruded first and second plastics materials includes gas bubbles so that the extruded elongate tubing has one of its first and second layers having gas bubbles dispersed within the plastics material to increase the visibility of the catheter under ultrasound imaging.
 34. Method of claim 33, further comprising the steps of: supplying a third plastics material to the extrusion machine; coextruding the third plastics material with the first and second plastics materials to form the tubing with a third outer layer of plastics material formed about said second layer; wherein the first inner layer and the third outer layer are substantially free of gas bubbles and the second layer has gas bubbles dispersed within its plastics material to provide the tubing with a smooth inner wall and a smooth outer wall.
 35. Method of claim 33, further comprising the step of: providing gas-filled polymer microspheres to the other of the first and second plastics materials to form gas bubbles in the other layer having a size in the range 0.1 μ to 300 μ.
 36. Method of claim 33, wherein the coextruding step comprises extruding the other layer of the tubing to be thicker than the one layer.
 37. Method of claim 33, wherein said medical device is a catheter and the elongate tubing of the catheter has one and other ends, the method further comprising the steps of: adding a hub to one of the one and other ends of the catheter; and rounding the other of the one and other ends to prevent trauma to the patient when the catheter is inserted into the patient.
 38. A method of monitoring the location of a medical device within a patient, comprising the steps of: placing within the patient a medical device having an elongate portion with a first inner layer of a plastics material and a second layer of a plastics material coextruded with one another so that said second layer is formed around the inner layer, wherein one of said first and second layers extruded being substantially free of gas bubbles and the other of said layers extruded includes gas bubbles dispersed in its plastics material to increase the visibility of the elongate portion under ultrasound imaging; and using an ultrasound imaging equipment to monitor the location of the medical device.
 39. Method of claim 38, wherein said medical device comprises a catheter with a through bore having a third layer of plastics material coextruded with said first and second layers, said third layer formed around said second layer, wherein said second layer includes the gas bubbles, and wherein the first inner layer has an inner wall that forms the through bore of said catheter.
 40. A catheter with a through bore usable under ultrasound imaging having an elongate portion consisting of an inner layer of plastics material, a middle layer of plastics material formed around said inner layer, and an outer layer of plastics material formed around said second layer; wherein said inner, middle and outer layers of plastics material are coextruded with each other from respective plastics materials with two of said layers extruded to be substantially free of gas bubbles and the remaining of said layers extruded to include gas bubbles dispersed in its plastics material, said inner layer having an inner wall that defines the through bore of said catheter; wherein the visibility of said catheter under ultrasound imaging is increased due to said catheter having a layer that has gas bubbles dispersed in its plastics material.
 41. The catheter of claim 40, wherein said inner layer and said outer layer are the two layers of said catheter that are substantially free of gas bubbles and said middle layer has the gas bubbles, so that said catheter consists of three layers with said second layer sandwiched between said inner and outer layers, wherein the inner wall of said inner layer and the outer wall of said outer layer provide said catheter with a smooth inner wall that defines its through bore and a smooth outer wall; and wherein said inner layer and outer layers each are thinner than said middle layer.
 42. An embryo transfer catheter with a through bore usable under ultrasound imaging having an elongate portion consisting of a first inner layer of plastics material and a second layer of plastics material formed around the inner layer, wherein said first and second layers of plastics material are coextruded with one another from respective plastics materials with one of said layers being extruded to be substantially free of gas bubbles and the other of said layers being extruded to include gas bubbles dispersed in said other layer, said inner layer having an inner wall that defines the through bore of said catheter, wherein the visibility of said catheter under ultrasound imaging is increased due to said catheter having a layer that has gas bubbles dispersed in its plastics material, and wherein the plastics materials are sufficiently transparent to ultrasound energy to enable an embryo moving along said catheter to be visualized under ultrasound imaging.
 43. The embryo transfer catheter of claim 42, wherein said second layer contains the gas bubbles and provides a main substrate of the catheter, and wherein said inner layer is thinner than said second layer and its inner wall provides a smooth wall for the bore of said catheter to reduce trauma to the embryo.
 44. An embryo transfer catheter with a through bore usable under ultrasound imaging having an elongate portion consisting of an inner layer of plastics material, a middle layer of plastics material formed around said inner layer, and an outer layer of plastics material formed around said second layer; wherein said inner, middle and outer layers of plastics material are coextruded with each other from respective plastics materials, wherein said outer and inner layers are extruded to be substantially free of gas bubbles and said middle layer is extruded to include gas bubbles dispersed in its plastics material to increase the visibility of said catheter under ultrasound imaging, said inner layer having an inner wall that defines the through bore of said catheter to provide a smooth wall for the bore; and wherein the plastics materials are sufficiently transparent to ultrasound energy to enable an embryo moving along the bore of said catheter to be visualized under ultrasound imaging. 